1. Field of the Invention
The present invention relates to a technique for suppressing spurious resonances in strip transmission line circuits and, more particularly, to a technique which displaces the spurious resonant frequencies outside the frequency band of interest by the addition of longitudinal slots in the capacitive elements of the strip transmission line circuits.
2. Description of the Prior Art
Strip transmission line circuits have been used in a variety of ways with the strip transmission line filter being the primary arrangement found. A typical prior art strip transmission line filter design is shown in U.S. Pat. No. 2,411,555 issued to D. C. Rogers on Nov. 26, 1946 which relates to a strip transmission line microwave filter including the general design of an L-C network comprising a pattern of alternate wide and narrow portions of conducting material similar to that of the present invention.
With such filters, undesired resonances can be introduced which should preferably be compensated for. For example, U.S. Pat. No. 3,879,690 issued to B. Golant et al on Apr. 22, 1975 relates to a distributed transmission line filter comprising a pattern of alternate wide and narrow symmetrical sections. In accordance with the Golant et al arrangement, an undesired resonance is prevented in a distributed transmission line filter comprising a center conductor having serially connected inductive and capacitive sections separated from a ground conductor by a dielectic substrate having a first thickness for filter inductive sections and a second thickness for at least one of filter capacitive sections.
Spurious sharp resonances can exist in the filters, and if excited by the circuit containing the filter, these modes can degrade the performance of the circuit. The problem remaining in the prior art, therefore, is to provide a technique for use with strip transmission line circuits which removes the spurious sharp resonances from the frequency band of interest to avoid performance degradation.